HS-40 is a 350-400 bp enhancer element located about 40 kb upstream of .zeta.-globin gene, which is expressed in the human embryonic erythroblasts but not in the human adult erythroblasts. Specific elements within the HS-40 enhancer have been identified, including GATA-1 motifs, NF-E2/AP1 motifs (a 3' and a 5' motif), and a Sp1 binding site.